Ajax confirmed on their
official website that Malen, 16, will move to North London immediately after turning down an offer to extend his deal with the Eredivisie side.
Ajax head of youth Wim Jonk said: "Donyell is a great talent. It is extremely unfortunate that he is leaving Ajax."
Donyell Malen (left) has represented Netherlands at youth level.
Jonk had earlier said in
Voetbal International: "We have made Donyell an excellent offer and presented a clear plan for his development.
"If the player still makes the decision [to leave], that's disappointing, because his potential is clear and he would be given opportunities with Ajax.
"We will continue with the guys who believe in the plan."
Malen, who is represented by agent Mino Raiola, played for Ajax's B1 youth team last season.